This invention relates to a motion picture camera. In particular it relates to a motion picture camera which is to have fade-over capabilities. In particular, the camera normally has a bridge circuit which includes a light-sensitive receiver whose resistance varies as a function of light impinging thereon. An unbalance in the bridge results in the applicaton of a control signal which causes a step motor coupled to the diaphragm to increase or decrease the aperture of the diaphragm in correspondence to the polarity and magnitude of the output signal from the bridge and until such time as the bridge output signal is again indicative of a balanced bridge.